[PATCH 1/2] drm/nouveau: fail runtime pm properly.

[Maarten Lankhorst]

BugLink: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1313986

If we were on a non-optimus device, we'd return -EINVAL, this would
lead to the over engineered runtime pm system to go into an error
state, subsequent get_sync's would fail, so we'd never be able
to open the device again.

(like really get_sync shouldn't fail if the device isn't powered
down).

Signed-off-by: Dave Airlie <airlied at redhat.com>
Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
(cherry picked from commit adbbdbac04f093c0abf946b1e93e4e5291808491)